Method of operating an internal combustion engine in particular in a motor vehicle

ABSTRACT

An internal combustion engine ( 1 ), in particular for a motor vehicle, is described; it is equipped with a catalytic converter ( 12 ) which may be exposed to nitrogen oxides. A lambda probe ( 13 ) is provided for measuring the oxygen concentration downstream from the catalytic converter ( 12 ). The nitrogen oxides supplied to the catalytic converter ( 12 ) are increased by a controller ( 18 ), and the conversion capacity of the catalytic converter ( 12 ) is concluded from the increase in oxygen concentration downstream from the catalytic converter ( 12 ).

BACKGROUND INFORMATION

[0001] The present invention relates to a method of operating an internal combustion engine of a motor vehicle in particular, a catalytic converter being exposed to nitrogen oxides, and the oxygen concentration being measured downstream from the catalytic converter. Likewise the present invention also concerns a controller for an engine of a motor vehicle in particular as well as an engine for a motor vehicle in particular.

[0002] Such a method, such a controller and such an engine are known, for example, with intake manifold injection, where fuel is injected into the intake manifold of the engine during the intake phase. Nitrogen oxides resulting from combustion of fuel are converted to nitrogen and oxygen in the catalytic converter. The catalytic converter is known to be subject to aging, which causes a decline in conversion capacity.

[0003] A method of the type defined above is also known for an internal combustion engine having direct injection. In this case, fuel is injected directly into the combustion chamber of the engine during the intake phase. The resulting nitrogen oxides are optionally stored temporarily in the downstream catalytic converters and then converted to oxygen.

OBJECT AND ADVANTAGES OF THE INVENTION

[0004] The object of the present invention is to create a method of operating an engine with which the aging of the catalytic converter is detectable.

[0005] This object is achieved by a method according to the present invention of the type defined in the preamble by increasing the nitrogen oxides supplied to the catalytic converter, and determining the conversion capacity of the catalytic converter from an increase in oxygen concentration downstream from the catalytic converter. The object is achieved accordingly with a controller and an internal combustion engine of the type defined in the preamble. The present invention is equally applicable with intake manifold injection and with an engine having direct fuel injection.

[0006] Increasing the nitrogen oxides supplied to the catalytic converter results in increased conversion of nitrogen oxides to nitrogen and oxygen. The resulting increase in oxygen concentration downstream from the catalytic converter is measured. The conversion capacity of the catalytic converter may be concluded from this increase.

[0007] With a new catalytic converter, the conversion capacity is high and the increase in oxygen concentration will also be high. With an aged catalytic converter, however, the increase in oxygen concentration will be diminished due to the diminished conversion capacity. This may be used as a measure of the conversion capacity and thus the aging of the catalytic converter.

[0008] Therefore, with the method according to the present invention for detecting the aging of the catalytic converter, no NOx sensor is necessary. This is a considerable cost saving. Likewise the required lambda probe for measuring the oxygen concentration downstream from the catalytic converter may also be used for other purposes, e.g., for controlling and/or regulating the engine, in particular for setpoint control, as it is known.

[0009] In an advantageous refinement of the present invention, the oxygen concentration upstream from the catalytic converter is kept constant. This achieves the result that only the elevated nitrogen oxide concentrations result in an increase in oxygen concentration downstream from the catalytic converter. However, the composition of the exhaust gas with respect to other components has no effect on the conclusion of catalytic converter conversion capacity according to the present invention.

[0010] In another advantageous refinement of the present invention, the lambda value is kept constant upstream from the catalytic converter. This also results in that only the elevated nitrogen oxides result in an increase in oxygen concentration downstream from the catalytic converter. This greatly simplifies the method according to the present invention.

[0011] In an advantageous embodiment of the present invention, the measured oxygen concentration downstream from the catalytic converter represents the oxygen concentration released by the catalytic converter from the nitrogen oxides supplied. This allows an especially simple and effective method of determining the conversion capacity of the catalytic converter.

[0012] It is especially advantageous if the increase in nitrogen oxides supplied to the catalytic converter is achieved by detuning of the ignition time and/or other interventions in the control and/or regulation of the engine. These options for modifying the nitrogen oxide feed to the catalytic converter are especially simple to implement and nevertheless very accurate. Repetition of the method according to the present invention and thus continuous diagnosis of the catalytic converter are thus readily possible.

[0013] Implementation of the method according to the present invention in the form of a control element provided for a controller of an engine in a motor vehicle in particular is particularly important. A program capable of running on a computer, in particular a microprocessor, and suitable for execution of the method according to the present invention is stored in the control element. In this case, the present invention is implemented via a program stored in the control element so that this control element equipped with the program represents the present invention in the same manner as the method for whose execution the program is suitable. An electric storage medium e.g., a read-only memory or a flash memory, may be used in particular as the control element.

[0014] Other features, possible applications, and advantages of the present invention are derived from the following description of exemplary embodiments of the invention illustrated in the drawing. All the features described or illustrated here form the object of the present invention either independently or in any desired combination, regardless of how they are combined in the patent claims or their reference back to a previous claim and regardless of how they are formulated in the description or illustrated in the drawing.

EXEMPLARY EMBODIMENTS OF THE INVENTION

[0015] The sole FIGURE in the drawing shows a schematic illustration of an embodiment of an engine according to the present invention.

[0016] The FIGURE shows an internal combustion engine 1 in a motor vehicle, where a piston 2 is movable back and forth in a cylinder 3. Cylinder 3 is equipped with a combustion chamber 4, which is delimited by piston 2, intake valve 5, and exhaust valve 6. An intake manifold 7 is connected to intake valve 5 and an exhaust pipe 8 is connected to exhaust valve 6.

[0017] An injector 9 is provided in intake manifold 7. A spark plug 10 protrudes into combustion chamber 4 in the area of intake valve 5 and exhaust valve 6. Fuel may be injected into intake manifold 7 through injector 9. The air/fuel mixture drawn in may be ignited in combustion chamber 4 by spark plug 10.

[0018] A rotatable throttle valve 11 is accommodated in intake manifold 7. The amount of air supplied to combustion chamber 4 depends on the angular setting of throttle valve 11. A catalytic converter 12 is provided in exhaust pipe 8 to purify the exhaust gas generated by combustion of fuel.

[0019] Catalytic converter 12 is provided so that nitrogen oxides (NOx) may be converted to nitrogen and oxygen. A continuous lambda probe 13 is provided in the exhaust pipe directly downstream from catalytic converter 12 and is suitable for measuring the free oxygen concentration O2free in the exhaust downstream from catalytic converter 12.

[0020] A controller 18 receives input signals 19 which are operating variables of engine 1 measured by sensors. Controller 18 generates output signals 20 with which the performance of engine 1 may be influenced via actuators and controlling elements. Controller 18 is provided so that, among other things, the operating variables of engine 1 may be controlled and/or regulated. To this end, controller 18 is equipped with a microprocessor which has a program suitable for executing this control and/or regulation stored in a memory medium, in particular in a flash memory.

[0021] Nitrogen oxides (NOx) generated during operation of engine 1 are supplied to catalytic converter 12. These nitrogen oxides are converted by catalytic converter 12 into nitrogen and oxygen. The ongoing conversion results in a diminished conversion capacity of catalytic converter 12; this is referred to hereinafter as aging.

[0022] Free oxygen concentration O2free downstream from catalytic converter 12 is composed of oxygen concentration O2Exhaust in the exhaust gas downstream from catalytic converter 12 and oxygen concentration O2Cat released from the nitrogen oxide feed by catalytic converter 12. Concentration O2Exhaust is in the per mill range, and concentration O2Cat is approximately in the ppm range.

[0023] Oxygen concentration O2Exhaust in the exhaust gas downstream from catalytic converter 12 depends on the oxygen concentration upstream from the catalytic converter and thus on the lambda value upstream from catalytic converter 12. For performing the diagnosis of catalytic converter 12 described below, the oxygen concentration upstream from catalytic converter 12 and thus the lambda value upstream from catalytic converter 12 are kept constant. The oxygen concentration O2Exhaust in the exhaust gas downstream from catalytic converter 12 is therefore constant.

[0024] Then the concentration or number of nitrogen oxides upstream from catalytic converter 12 is increased. This may be accomplished, for example, by detuning the ignition time of individual cylinders or by similar measures.

[0025] Because of the increased nitrogen oxide concentration upstream from catalytic converter 12, an increased conversion of nitrogen oxides to nitrogen and oxygen is performed by same. This results in an increased oxygen concentration O2Cat released from the nitrogen oxide feed by catalytic converter 12. This increased concentration O2Cat in turn results in an increased free oxygen concentration O2free downstream from catalytic converter 12.

[0026] Increased free oxygen concentration O2free downstream from catalytic converter 12 is measured by continuous lambda probe 13 downstream from catalytic converter 12. Since oxygen concentration O2Exhaust in the exhaust gas downstream from catalytic converter 12 is kept constant, increased free oxygen concentration O2free measured by lambda probe 13 represents directly the increase in oxygen concentration O2Cat released from the nitrogen oxide feed by catalytic converter 12.

[0027] The diagnostic method described above is performed by controller 18 at preselected intervals in time and/or on the basis of preselected events. This results in a series of successive measurement results for increased concentration O2free representing the increase in concentration O2Cat, as stated above.

[0028] As already mentioned, the conversion capacity of catalytic converter 12 declines over time due to aging. This decline in conversion capacity results in concentration O2Cat also declining over time in the measurement results performed as described above. Concentration O2Cat is to this extent a measure of the conversion capacity and thus the aging of catalytic converter 12.

[0029] Finally, controller 18 concludes the conversion capacity and thus the aging of catalytic converter 12 on the basis of the individual measurement results and the curve of successive measurement results for concentration O2free. This is achieved, for example, by monitoring the change in concentration O2free. It is likewise possible to monitor the absolute values of concentration O2free and to compare them with the values of a new catalytic converter, for example. All these comparisons may be performed by controller 18 either individually or in combination. Thus, on the whole, it is possible for controller 18 to conclude the aging or aging condition of catalytic converter 12. If this aging exceeds a preselected threshold value, this is indicated to the operator of engine 1 by controller 18. 

What is claimed is:
 1. A method of operating an internal combustion engine (1), in particular in a motor vehicle, a catalytic converter (12) being exposed to nitrogen oxides, and the oxygen concentration (O2free) downstream from the catalytic converter (12) being measured, wherein the nitrogen oxides supplied to the catalytic converter (12) are increased, and the conversion capacity of the catalytic converter (12) is concluded from the increase in the oxygen concentration (O2free) downstream from the catalytic converter (12).
 2. The method according to claim 1, wherein the oxygen concentration (O2Exhaust) upstream from the catalytic converter (12) is kept constant.
 3. The method according to one of claims 1 or 2, wherein the lambda value upstream from the catalytic converter (12) is kept constant.
 4. The method according to claim 2 or 3, wherein the measured oxygen concentration (O2free) downstream from the catalytic converter (12) represents the oxygen concentration (O2Cat) released by the catalytic converter (12) from the nitrogen oxides supplied.
 5. The method according to one of claims 1 through 4, wherein the concentration (O2Cat) is used as a measure of the conversion capacity of the catalytic converter (12).
 6. The method according to one of claims 1 through 5, wherein the increase in nitrogen oxides supplied to the catalytic converter (12) is achieved by detuning the ignition time and/or through other measures in the control and/or regulation of the internal combustion engine (1).
 7. A control element, in particular a flash memory, for a controller (18) of an internal combustion engine (1) in a motor vehicle in particular, a program being stored on it, capable of running on a computer, in particular a microprocessor, and suitable for execution of a method according to one of claims 1 through
 6. 8. A controller (18) for an internal combustion engine (1) of a motor vehicle in particular, the engine (1) having a catalytic converter (12) which may be exposed to nitrogen oxides, and having a lambda probe (13) for measuring the oxygen concentration (O2free) downstream from the catalytic converter (12), wherein the controller (18) is capable of increasing the nitrogen oxides supplied to the catalytic converter (12), and the controller (18) is capable of determining the conversion capacity of the catalytic converter (12) on the basis of the increase in oxygen concentration (O2free) downstream from the catalytic converter (12).
 9. An internal combustion engine (1) for a motor vehicle in particular, having a catalytic converter (12) which may be exposed to nitrogen oxides, and having a lambda probe (13) for measuring the oxygen concentration (O2free) downstream from the catalytic converter (12) and having a controller (18), wherein the controller (18) is capable of increasing the nitrogen oxides supplied to the catalytic converter (12) and of concluding the conversion capacity of the catalytic converter (12) on the basis of the increase in oxygen concentration (O2free) downstream from the catalytic converter (12). 